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Developing a Permanent BMP Strategy

This section covers the development of a permanent BMP strategy, including site design principles, DPP BMPs, and treatment BMPs. It also discusses the use of infiltration areas as treatment BMPs and provides guidance on tracking treated areas.

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Developing a Permanent BMP Strategy

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  1. Section 5 – Permanent BMPs • A permanent BMP strategy should: • Maximize infiltration • Prioritize Treatment BMPs • Provide detailed documentation of treatment • Permanent BMPs include: • Design Pollution Prevention (DPP) BMPs • Permanent soil stabilization and concentrated flow controls • Treatment BMPs • Permanent treatment devices and facilities • DPP BMP consideration required for all projects with DSA. • Treatment BMP consideration required per EDF. Brown and Caldwell

  2. Section 5 - Overview • This section will cover: • Developing a permanent BMP strategy • Site design principles • DPP BMPs • DPP infiltration for treatment • Infiltration Tool • Checklist T-1, Part 1 Review • WQV and WQF • Treatment prioritization • Documenting treatment Brown and Caldwell

  3. Section 5 – Developing a Permanent BMP Strategy • Consider: • Site design principles • DPP BMPs • Treatment BMPs Site design principles include: Conserve natural areas, minimize disturbance to natural drainages Design for soil conditions and slope! Vegetated strips and swales Minimize impervious footprint Brown and Caldwell Pervious areas receive runoff from impervious area

  4. Section 5 – DPP BMPs DPP BMP Consideration Form Checklist DPP-1, Part 1. If any Checklist DPP-1, Part 1 question is answered Yes, DPP BMPs are required. Document in Section 6 of the SWDR. Brown and Caldwell

  5. Section 5 – DPP BMPs DPP BMPs that provide infiltration can be documented as treatment, including vegetated and non-vegetated areas. • Which of these DPP BMPs could provide infiltration for treatment credit? • Worst one? • Best one? Note: If any DPP BMP creates concentrated flows, refer to HDM Chapter 860. Consider channel lining when appropriate. Brown and Caldwell

  6. Section 5 – DPP Infiltration Areas • DPP Infiltration Areas: • Vegetated and non-vegetated areas • Sized to capture WQV • New, modified, or existing areas • Areas must be stabilized to prevent erosion • Areas can be amended • Areas do not necessarily meet the design requirements of Biostrips or Bioswales • Use Checklist T-1, Part 11 Brown and Caldwell

  7. Section 5 – DPP Infiltration Areas as Treatment BMPs DPP Infiltration Areas are evaluated and tracked as Treatment BMPs Brown and Caldwell

  8. Section 5 – Infiltration Tool Strip and Swale Infiltration Tool (SSIT) Basin Infiltration Tool (BIT) Brown and Caldwell

  9. Section 5 – Infiltration Tool – SSIT Input Brown and Caldwell

  10. Section 5 – Infiltration Tool – SSIT Input Brown and Caldwell

  11. Section 5 – Infiltration Tool – Output If < 100%, consider amending soil Brown and Caldwell

  12. Section 5 – Infiltration Tool – Amendments Brown and Caldwell

  13. Section 5 – Infiltration Tool – Amendments Use for Checklist T-1, Part 1 Question 2 and document in Table E-2. Brown and Caldwell

  14. Section 5 – Infiltration Tool The SSIT Results tab produces a design summary report. Brown and Caldwell

  15. Section 5 – Treatment Tracking, include all BMPs Track all areas treated by DPP BMPs using Table E-2 If additional treated area required, consider other Treatment BMPs Brown and Caldwell

  16. Section 5 –Treatment BMPs Use the EDF to determine if Treatment BMPs are required then use Checklist T-1, Part 1 to evaluate Treatment BMPs. Use to support narrative of Section 6 in the SWDR. • Infiltration Rules! • Biofiltration encouraged • TDCs simply 4 Matrices If approved Treatment BMPs are not feasible, consult with SW Coordinator. May be able to use non-approved BMPs as pilot projects if approved. Brown and Caldwell

  17. Section 5 – T-1, Part 1 Consider Treatment BMPs How do we calculate WQV and WQF for use in T-1, Part 1? Brown and Caldwell

  18. Section 5 – Identify Potential Treatment Areas Potential BMP Area Brown and Caldwell

  19. Section 5 – Delineate CDA Contributing Drainage Area Brown and Caldwell

  20. Section 5 – WQV, Volume-Based Runoff Coefficient (RV) Brown and Caldwell

  21. Section 5 – WQV, Volume-Based Runoff Coefficient (RV) When 50% o more of impervious surfaces drain from impervious to pervious, use Table 5-2 or calculate coefficient directly using Urbonas (1999) equation Three scenarios where a composite VR calculation is required: CDAs with hydraulically separated pervious and impervious areas CDAs where impervious surfaces are less than 50% of the drainage area 3. CDAs where pervious area drains to impervious Where: VR1 = WQV impervious VR2 = WQV pervious Brown and Caldwell

  22. Section 5 – WQV, Volume-Based Runoff Coefficient (RV) Brown and Caldwell

  23. Section 5 – WQV, Volume-Based Runoff Coefficient (RV) Brown and Caldwell

  24. Section 5 – WQV Example • Given: • Sacramento County • Potential drainage (shown), is 0.3-mile (1,633 ft) long with 2 new lanes, a shoulder, and an embankment • Average overland slope of the flow path is 1%. • 85th percentile, 24-hour rainfall depth is 0.62 inch • Potential BMP requires volume-based sizing. Brown and Caldwell

  25. Section 5 – WQV Example • Solution: • Step 1: Calculate Areas • The CDA consists of 2 travel lanes, a shoulder, and the embankment: The percent impervious for the CDA is calculated: Brown and Caldwell

  26. Section 5 – WQV Example • Solution: • Step 2: Volumetric Runoff Coefficients • Because the CDA drains impervious to pervious and the impervious is 50%, use Table 5-2 to determine RV for the CDA. RV = 0.34 Brown and Caldwell

  27. Section 5 – WQV Example Solution: Step 3: Water Quality Volume Where, RV = 0.34 (from Step 2) P = 0.62 in (from problem statement) A = 2 acres (from Step 1) Brown and Caldwell

  28. Section 5 – WQF, Flow-Based Runoff Coefficient NOTE: Continue to use runoff coefficients from HDM Chapter 831 to develop Design Storm flows. Brown and Caldwell

  29. Section 5 – WQF Example • Given: • Sacramento County • Potential drainage (shown), is 0.3-mile (1,633 ft) long with 2 new lanes, a shoulder, and an embankment • Rainfall intensity from Basin Sizer is 0.16 in/hr • Potential BMP requires flow-based sizing. Brown and Caldwell

  30. Section 5 – WQV Example Solution: Step 1: Calculate Areas The pervious area is: The impervious area is: Brown and Caldwell

  31. Section 5 – WQF Example • Solution: • Step 2: Flow-Based Runoff Coefficients • Using Table 5-3 coefficients: Composite runoff coefficient: Brown and Caldwell

  32. Section 5 – WQF Example Solution: Step 3: Calculate WQF Where, (from Step 2) (from problem statement) (from Step 1) Use the WQV/WQFs calculated for potential BMPs to continue T-1, Part 1 Brown and Caldwell

  33. Section 5 –Checklist T-1, Part 1 Identify Treatment BMPs until Table E-1 PCTA Balance Continue through Checklist T-1, Part 1 to consider Treatment BMPs to meet TMDL requirements. Brown and Caldwell

  34. Section 5 –Checklist T-1, Part 1 Brown and Caldwell

  35. Section 5 – T-1, Part 1 Brown and Caldwell

  36. Section 5 – T-1, Part 1 Brown and Caldwell

  37. Section 5 – T-1, Part 1 Brown and Caldwell

  38. Section 5 – T-1, Part 1 Brown and Caldwell

  39. Section 5 – T-1, Part 1 Brown and Caldwell

  40. Section 5 – T-1, Part 1 Brown and Caldwell

  41. Section 5 – T-1, Part 1 Brown and Caldwell

  42. Section 5 – T-1, Part 1 Treatment Tracking Brown and Caldwell

  43. Section 5 – Project Treatment Summary Use Table E-1 to summarize all impervious areas treated project BMPs. Document in Section 1 of the SWDR. Don’t forget to include DPP BMPs that infiltrate. If PCTA Balance < 0 and additional treatment cannot be provided, document Alternative Compliance strategy in SWDR. Brown and Caldwell

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